Divide.
Explanation: There are many ways to solve this problem. Let's see two ways we could divide. Place value strategy We can think in terms of tenths: $\begin{aligned} 84 \div 0.1&= 84.0 \div 0.1\\\\ &= 840\text{ tenths} \div 1\text{ tenth}\\\\ &= 840 \end{aligned}$ Fraction multiplication strategy Decimals are a kind of fraction, so we can use fraction multiplication. $\begin{aligned} &\phantom{=}84 \div 0.1 \\\\ &= \dfrac{84}{0.1}\\\\ &= \dfrac{84 \times 10}{0.1 \times 10}\\\\ &= \dfrac{840}{1}\\\\ &= 840 \end{aligned}$ The answer $840 = 84 \div 0.1 $